The present application is a national stage filing under 35 U.S.C. xc2xa7371 of PCT/JP01/08671 filed on Oct. 2, 2001, and designating the U.S.
The present invention relates to a polishing material, and particularly to additives contained in constituting a polishing material having, as a major component, rare earth oxides including cerium oxide, composing such a polishing material.
Recently, glass materials are widely utilized, and used in numerous areas such as not only optical lens applications, but also optical and magnetic disc applications, color filters for liquid crystals, LSI photomasks, and others. Glass; materials for these applications require the smoothness of the surface with strictly high accuracy, and therefore polishing materials having, as the major component, rare earth oxides including cerium oxide have been conventionally employed for processing their surface.
These polishing materials having, as the major component, rare earth oxides including cerium oxide are generally used in a slurry state, in which the abrasive grains of a polishing material are dispersed into a dispersion medium such as water. When a polishing material in this slurry condition is allowed to stand, the dispersoid, abrasive grains of the polishing material, is easily separated from the dispersion medium, causing a phenomenon of precipitation.
In addition, polishing materials are used with cycling, so that the abrasive grains themselves will be ground and a glass component of a substrate to be polished will be included, and when the abrasive grains are precipitated, the precipitates tend to become very hard.
Such separation and precipitation of the abrasive grains will disable the composition of a slurry having a given concentration or the concentration from being maintained while use with cycling, thereby decreasing the efficiency of polishing. When the abrasive grain precipitates become hard, the abrasive grains tend to readily adhere onto the glass surface of a substrate to be polished, and operations are required for removing the abrasive grains from the glass surface; so-called washing property on the glass surface will be thus impaired. Furthermore, the hardening of the abrasive grain precipitates tends to result in a clogged polishing pad, which will be also a cause of forming scratches on the surface of a substrate to be polished.
Under the present condition, the above described problems in polishing glass materials are also pointed out for chemical mechanical polishing (CMP) conducted in a semiconductor manufacturing process.
In order to solve the problems of abrasive grain precipitates in a polishing slurry as described above, many proposals have been conventionally made for additives contained in constituting a polishing material.
For example, as additives for preventing abrasive grain precipitates from hardening, there have been proposed ammonium phosphate salt (Japanese Patent Application Laid-Open No. 56-147880) and phosphate salts of rare earth metals (Japanese Patent Application Laid-Open No. 56-45975), magnesium chloride (Japanese Patent Application Laid-Open No. 3-14658:5), calcium compounds (Japanese Patent Application Laid-Open No. 6-330025), amino acids and amines (Japanese Patent Application Laid-Open No. 10-183104).
These additives for polishing materials are effective in terms of redressing the hardness of the abrasive grain precipitates, but not sufficiently satisfactory in terms of the dispersibility of the abrasive grains in a dispersion medium and the accompanying efficiency of polishing. Accordingly, further improvement is needed in the present circumstances.